The present invention generally relates to wiring of electronic apparatus and more particularly to a connecting structure of conductors used for connecting conductors in an electronic apparatus such as a semiconductor device.
In a semiconductor device such as an integrated circuit, there are cases that a conductor used for wiring at one side of an insulator layer is connected to another conductor at the other side of the insulator layer. For that purpose, a connecting part is formed, contactings the two conductors, extending through the insulator layer.
When the semiconductor device is used, such a connecting part tends to invite a concentration of electron flow which causes an electromigration in the conductor. The electromigration is a phenomenon in which an atom of the conductor is displaced from its original position by the impact of electron flowing in a direction. The electromigration of aluminium is well known. When the electromigration proceeds excessively, a large number of atoms of the conductor at the connecting part are displaced by the impacting electrons and the contact between the two conductors is degraded or lost. In other words, the connecting part is destroyed by an electron current or flow, and the two conductors are disconnected. Such a disconnection of the wiring in the semiconductor device limits the lifetime of the semiconductor device.
As the rest of the part of the semiconductor device is still capable of continuing its operation, the lifetime of the semiconductor device can be extended when the lifetime of the connecting part is extended. For this purpose it is necessary to solve the problem of degradation of the contact by the electromigration.
In order to reduce the effect of electromigration, it is desired to reduce or minimize the concentration of electron flow passing through the connecting part at a particular location of the connecting part.
Conventionally, there is a connecting structure comprising numerous contacting parts disposed in a row and column formation with a substantial mutual separation such that the contacting parts are aligned alternately. Such a structure, though capable of reducing the electromigration effect, has a limitation in that the conductor to be connected should have a relatively large width. For example, a width of about 100 .mu.m or more is required for the conductor when a pair of conductors are connected by three or four rows of connecting parts each including two or three connecting parts with a size of about 10 .mu.m.times.10 .mu.m. Thus, such a conventional connecting structure cannot be used for wiring patterns having a conductor with a substantially small width such as 50 .mu.m or less.
Further, there is a known connecting structure in which a pair of conductors at both sides of an insulating layer make a contact at a plurality of contacts which are aligned in a plurality of rows extending in a direction of flow of electron. In one construction shown in FIG. 1, two rows of contacts 1 and 2 each including three or more contacts 1a-1c, 2a-2c therein are provided in which the size of the contact is made identical except for the first contact 1a, 2a, at a most upstream side of a flow of electron e, which is made to have a smaller width than the rest of the contacts in the row. In such a construction, there is a problem that the electron flow e is mainly concentrated to the first contact(s) 1a, 2a having the small size although some of the electrons are received by a part of the second contact(s) 1b, 2b extending into a path of the flow of electron beyond the small sized first contact(s) 1a, 2a, and the first contact(s) becomes defective after a short period of time. This is because the third contact(s) 1c, 2c having the size identical to the size of the second contact 1b, 2b is in the shadow of the flow of of electron formed behind the second contact(s) and does not contribute to the conduction of the electron flow e. Once the first contact is gone, the second contact behind the first contact is subjected to the heavy concentration of the electron flow and becomes defective after a short period of time. After the second contact, the third contact becomes defective similarly. Thus, such a conventional connecting structure, provides only a limited lifetime.